This application is directed to methods and apparatus for data hiding in an image and, more particularly, to lossless data hiding using the integer wavelet transform.
In the field of data hiding, pieces of information represented by the data are hidden in the cover media (e.g., a pixel image). In some applications, people care about whether the embedded data are perceptible with the cover media. That is, the hidden data and the cover media may be closely related. For this type of data embedding, it may be desirable to invert the marked media back to the original cover media after the hidden data have been retrieved. For example, perceptual transparency and inversion of marked media may be desirable for applications such as medical diagnosis and law enforcement. The marking techniques satisfying these requirements are referred to as lossless, distortion-free, and reversible or invertible data hiding techniques.
Although most of the current digital watermarking algorithms are not lossless, some recent marking techniques have been reported as being lossless. For example, two methods carried out in the image spatial domain purport to be lossless. The details of these methods may be found in U.S. Pat. No. 6,278,791 (the entire disclosure of which is hereby incorporated by reference) and J. Fridrich, M. Goljan and R. Du, “Invertible Authentication,” Proc. SPIE, Security and Watermarking of Multimedia Contents, pp. 197-208, San Jose, Calif., (January 2001). A purportedly lossless marking technique has also been developed in the transform domain, as is discussed in detail in B. Macq and F. Deweyand, “Trusted Headers For Medical Images,” DFG VIII-D II Watermarking Workshop, Erlangen, Germany, (October 1999). As these techniques are directed toward data authentication, instead of data embedding, the amount of hidden data that may be achieved is quite limited. Another lossless marking technique that may be suitable for some higher quantities of data embedding has also been developed and is discussed in detail in U.S. Patent Application No.: 2003/0081809 (the entire disclosure of which is hereby incorporated by reference). The amount of hidden data achievable by this technique, however, is still not large enough for many applications, such as medical applications. Indeed, the pay-load ranges from 3,000 bits to 24,000 bits for a 512×512×8 grayscale image.
Accordingly, there are needs in the art for new methods and apparatus for achieving lossless marking that can embed a relatively large amount of data.